The present invention relates to a new and improved method for feeding a large volume of electrical components to a vision controlled robotic placement apparatus. More particularly, it relates to an improved carrier tape and feeder which are responsive to an optical sensor and to directions from the vision system of the robot to provide a large number of electrical components to a robot placement apparatus in a low cost, lost space requirements operation.
Reeled carrier assemblies for transporting and supplying a large number of electronic components are known. The carrier assembly typically comprises a flexible substrate tape including a plurality of spaced apart component receiving pockets which extend transversely across the tape. The pockets are provided in spaced apart parallel relationship along the length of the tape. The component receiving pocket may be vacuum formed to receive particular electronic components in a dedicated orientation. A releaseable cover tape is applied to the top surface of the carrier substrate tape to retain the electronic components in the pockets. The covered carrier tape can be wound upon a reel until it is unreeled for further processing. Carrier assemblies of this type can support several thousand electronic components in a very compact manner.
Carrier tape assemblies have been used in the past to feed a large number of components to a pick up station where they are picked up by a robotic assembly apparatus and positioned in an appropriate location on a printed circuit substrate. In these prior art robotic assembly machines, a tape indexer mechanically positions a component receiving cavity at a precisely located pick up station for pick up by a robot arm. Exact positioning of the component at the pick up station in these mechanically controlled delivery systems is extremely important so that the programmed robot may always find the electronic part and grasp it at desired locations. The robot arm relies upon the fact that the part will always be exactly located within its grasp, so that it can place the component in an exact location on a printed circuit board. The carrier tape must be prepared with needed accuracy to ensure accurate robotic placement of parts onto the printed circuit board.
To ensure precise mechanical indexing of the parts to the robotic pick up station, the carrier tapes are carefully prepared to accurately provide the component receiving pockets at equally spaced distances along the tape. Moreover, sprocket feeding holes must be precisely positioned on the edges of the tape with respect to each other and with respect to the component receiving pockets. The prior art carrier tapes are generally fed by a mechanical sprocket indexer which relies upon the inherent information stored in the tape to guarantee that a pocket and therefore a single part contained therein is precisely positioned at a robotic pick up station.
In these mechanical indexer arrangements, the cost of providing the precise carrier tape packaging is undesirably high. The sprocket holes and vacuum formed contoured component receiving pockets must be formed at precise locations along the tape within extremely close manufacturing tolerances which increases the cost of manufacture. Illustrative examples of prior mechanically indexed sprocket-hole carrier tapes and indexing feeders for use therewith are shown in U.S. Pat. No. 4,633,370 and U.S. Pat. No. 4,610,083, as well as, European publication No. EP0223505-A.
Visual guidance systems for controlling robot arm movements are now also known. A visual guidance or control system includes image receiving means typically in the form of a video camera which is capable of receiving an image and transmitting it to analyzing vision control equipment. The camera or other image obtaining means is typically mounted on the end of a robot arm to provide visual information about the locations adjacent the end of the arm. The image may be digitized and/or analyzed by vision control programming and equipment to provide guidance instructions to the robotic drive means controlling the movement of the robotic arm.
Visually guided robot arms have been used in robotically assembling electrical components to printed circuit boards. In these prior art arrangements, parts are fed to a robotic pick up station in organized rigid trays. The trays include a rigid tray substrate provided with a predetermined matrix of discrete pockets for receiving a number of components to be mounted on the printed circuit board. The parts are loaded into the pockets one part per pocket, all in the same orientation. Alternatively, the rectangular tray can include a plurality of elongate spaced apart troughs extending the length thereof into which a linear array of electrical components are positioned for pick up.
In accordance with these prior art arrangements, an individual operator loads a filled tray onto a loading apparatus which then automatically moves the loaded tray to a pick up station to positively position the tray in the pick up station. The visually guided robot then picks the parts from the tray one at a time and places them on a printed circuit board. In most of these prior art methods, the positive positioning of the tray, and therefore its pockets and packaged components, guarantees the mechanical positioning of the part for the robot arm. The visual guidance systems on these robot arms are used alone or in combination with fiducial marks provided on the target printed circuit substrates to aid the robot in properly positioning the part on the printed circuit board. The emphasis for using the visual guidance system has been for part mounting accuracy as opposed to parts acquisition.
A number of disadvantages for the prior art tray arrangement exist. The trays themselves only hold a limited number of parts. They take up a large amount of real estate or area immediately adjacent the robotic arm, especially in view of the limited number of parts that can be delivered. A separate loaded tray indexing apparatus is needed which adds considerably to the cost of using the trays.
U.S. Pat. No. 4,527,326 describes a visually guided robotic system for guiding a robot arm which indentifies and locates properly oriented or particular parts from among many parts presented along a delivery track extending from a vibratory bowl feeder.
Prior art carrier tape feeders which unreel a carrier tape and peel or pull back the adhesively applied cover tape before indexing the tape to present one pocket at a time at a pick up station are known, from the above-identified patents and numerous other citations. They all rely on sprocket feed holes and mechanical indexing sprocket drive means for indexing the tape one pocket at a time, with the above mentioned disadvantages. The use of vision control systems for accurately placing parts on a printed circuit board is now well known however, vision control systems have the capability of accurately guiding a robot arm to acquire parts as well, and this capability has not been fully exploited.
Accordingly, it is desireable to incorporate the advantageous features of carrier tape supply assemblies including their ability to successively provide a large number of parts at a pick up station without taking up alot of space immediately adjacent a robot, but without the associated packaging costs. It is also desireable to incorporate some of the features of the prior art tray arrangements including their ability to provide a plurality of components per pocket and to use the visual guidance system on a robot arm for parts acquisition as well as parts placement but without the associated cost and manpower requirements previously associated with tray feeds.